Mammographic breast density is a strong predictor of breast cancer risk. At this present time, little is known about which attribute(s) of mammographic density also contributes to breast cancer risk. To gain insight into this question this Program Project Grant seeks to use human tissue to explore the biologic connection between mammographic density and molecular markers for breast cancer risk. To accomplish these goals, the Core will provide services that are fundamental to all projects within the Program Project Grant application. The primary goals of the Tissue and Biostatistics Core are to process breast tissue for study by the Program Project Investigators and provide high quality characterization and biostatistical analysis of samples. Core personnel will process fresh tissue from donors in a systematic manner, which will allow correlation of tissue blocks with density images for Projects 1 and 2. The Core will coordinate routine tissue processing, embedding, sectioning and staining through the UCSF Comprehensive Cancer Center Tissue Core. Routine immunohistochemistry stains for Projects 2 and 3 will be coordinated though the UCSF Comprehensive Cancer Center Immunohistochemistry and Molecular Pathology Core. Core pathologists will be responsible for the interpretation of H&E sections and immunohistochemistry stains. The Core biostatistician will be involved in study design and statistical analyses of data obtained by Projects 1, 2, 3, and 4.